Pores, which have remarkable influence on many properties of coatings such as wear resistance, anti-corrosion, thermostability, etc. are the natural structure formed in plasma sprayed coatings, and have been regarded as one of the most important indexes in spraying parameter refining. Hence, it is of great significance to comprehensively characterize the structural parameters of pores in the coatings, especially for the accurate evaluation of the coating quality. In this paper, probability statistics method, fractal method and digital image analysis technique are used to investigate the number, shape, size and distribution of the pores. Besides, the formation mechanism of the coatings is discussed. First, Fe-based coatings with different porous structures are fabricated at different spraying powers. Second, the digital image analysis technique is used to process the scanning electron microscope micrographs of coatings with different pores. Finally, the Weibull statistical model is utilized to analyze the distribution law of perimeter and area of the pores. The power law of area-perimeter which originats from fractal theory is employed to quantitatively characterize the irregular morphology of the pores. In order to investigate the formation mechanism of the pores, the Spraywatch is used to monitor the flying condition of the spraying particles in the whole experimental process. The result shows that fractal dimension (FD) can characterize the irregular morphology of pores. The area becomes bigger and the border becomes more complex when the FD is larger, and there is a good relationship between FD and the formation mechanism of the pores. Besides, the areas and perimeters of the pores obey the binomial Weibull distribution obviously, namely, the shape parameter (β) turns larger as pore size becomes smaller. The spraying power has a different effect on the distribution law of pore size. With the increase of the spraying power, the molten state is improved. As a result, the size of the pore decreases obviously. When the area or the perimeter is less than their corresponding characteristic values, the probability density of the pores with the same area or perimeter becomes closer to each other, which indicates that the effect of spraying power on the pores of small size is much lower.